The earliest indisputable arvicolines are represented by early Pliocene fossils in Holarctic North America, Europe and NW Asia (the primitive Prosomys; Chaline et al., 1999; Fejfar, 1990a; Repenning, 1998, 2003, as Promimomys). Southern Asia was not populated by voles until the late Pliocene, presumably derived from immigration of a European Mimomys stock (Kotlia, 1994; Kotlia and Koenigswald, 1992); early Pliocene dispersion of Mimomys to North America, via Beringia, important to the diversification of New World arvicolines (Repenning, 2003). Several independent lineages of cricetids with rooted, slightly hypsodont molars appeared in the late Miocene of Europe, Asia, and North America and survived into the Pleistocene in Europe; these "microtoid cricetids," such as Baranomys and Microtoscoptes, are believed to precede the appearance of true voles and were replaced by them (see review by Fejfar, 1999a). Although some have treated certain of these genera as Arvicolinae (e. g., Gromov and Polyakov, 1977; Kretzoi, 1969; Repenning, 1998; Repenning et al., 1990; Zheng and Li, 1990), most have recognized them as dentally progressive cricetids that exploited a graminivorous niche (see review by Chaline et al., 1999). Arvicolines are convincingly derived from a cricetid ancestral stock (Gromov and Polyakov, 1977; Kretzoi, 1955; Michaux et al., 2001b), yet whether their phylogenetic roots are embedded in the microtoid cricetids or another cricetid lineage is unknown. Chaline et al. (1999:242) summarized the uncertainty of the paleontological evidence: "there is a wide array of cricetids with arvicoline features but it is currently impossible to specify their involvement in the origin of arvicolines."

Notwithstanding the proliferation of family-group names, practically a one-to-one correspondence with recognized genera, suprageneric relationships remain somewhat ambiguous—e.g., compare the tribal contents of Ognev (1963), Hooper and Hart (1962), Kretzoi (1969), Gromov and Polyakov (1977), and Repenning (1992). The instability of tribal limits is mirrored in the irresolvable polytomies disclosed in phylogenetic evaluation of mitochondrial DNA sequences, suggesting rapid taxonomic diversification over a short time period (Conroy and Cook, 1999). In general, we follow McKenna and Bell (1997) for tribal affiliations (Table 1) and provide explanations for departures from their taxonomic scheme. We observe Ketzoi’s (1969) Myodini, type genus Myodes, for most arvicolines with rooted molars and simple molar patterns. In the following generic and specific remarks, therefore, readers should understand that wherever we use Myodes or Myodini the cited publications generally refer to Clethrionomys (or Evotomys) and Clethrionomyini.